If you've been following the Slender Man story, both teenagers involved in the attempted murder of Payton Leutner have now pled not guilty by reason of insanity. Based on what has been reported about the attempted murder, that sounds about right as no rational explanation exists for the horrifying actions.
Payton Leutner was invited to a sleepover at a classmate's house along with one other classmate. The following day, while out in a park, the two other girls, then only 12 years old, attacked, stabbed, and attempted to murder Leutner. Fortunately, she was able to escape, and she has now recovered from her physical injuries.